Tyre

ABSTRACT

A tyre, wherein the tread has a number of raised blocks divided into a number of elements by sipes crosswise to a motion direction of the tyre; wherein each element has at least a first lateral surface separated by a sipe from a second lateral surface of an adjacent element and having at least one first portion sloping with respect to the motion direction and facing a second portion of the second surface; and wherein parting of the first and second portion in the motion direction is controlled by an elastic locking device for locking the two portions to each other.

TECHNICAL FIELD

The present invention relates to a tyre.

BACKGROUND ART

Tyres are known in which the tread has circumferential and transversegrooves defining a number of blocks, at least some of which have, on theouter surface, a number of sipes substantially crosswise to the motiondirection of the tyre. The sipes, which divide the relative blocks intorespective numbers of relatively flexible elements crosswise to themotion direction of the tyre, serve not only to break up the film ofwater on wet road surfaces, for better tyre-ground contact in the rain,but also, and above all, to trap snow, by flexing, between adjacentelements to improve traction, braking, and lateral stability on snow.

While improving grip of the tyre on wet road surfaces or snow, sipedblocks, on the other hand, obviously have the drawback—given theflexibility of the relative elements, and especially on dry roadsurfaces—of impairing tyre performance in terms of handling capacity,traction, and braking.

To control deformation of the elements with respect to the adjacentelements when subjected to lateral forces, EP-1 073 562 proposesincreasing friction between two surfaces of adjacent elements separatedby a sipe, by imparting mating three-dimensional shapes to the surfaces.More specifically, projections are formed on each of the two surfaces,and each engage a respective cavity on the other surface.

Such a solution allows control of transverse deformation of theelements, i.e. along the relative sipes, but not of longitudinaldeformation of the elements, i.e. crosswise to the relative sipes.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a tyre designed tominimize the aforementioned drawback, while still maintaining the samewet and/or snow traction characteristics.

According to the present invention, there is provided a tyre as claimedin the attached independent Claim and, preferably, in any one of theClaims depending directly or indirectly on said independent Claim.

BRIEF DESCRIPTION OF THE DRAWINGS

A non-limiting embodiment of the present invention will be described byway of example with reference to the accompanying drawings, in which:

FIG. 1 shows a plan view of a tread portion of a preferred embodiment ofthe tyre according to the present invention;

FIG. 2 shows a larger-scale, schematic exploded view of a preferredembodiment of a detail in FIG. 1;

FIGS. 3 and 4 show sections of the FIG. 2 detail in a non-deformed anddeformed configuration respectively.

BEST MODE FOR CARRYING OUT THE INVENTION

Number 1 in FIG. 1 indicates as a whole a tyre with a tread 2 having anumber of raised blocks 3 divided into a number of elements 4 by sipes 5oriented in a direction substantially crosswise to a motion direction 6of tyre 1.

In connection with the above, it should be stressed that the term“motion direction” is intended to mean the instantaneous displacementdirection of the tyre, and not the travelling direction of the relativevehicle. Motion direction 6, therefore, though shown parallel to anequatorial plane of tyre 1 by way of example, may be variously orienteddifferently from the one shown.

Each element 4 has at least one lateral surface 7, which extends along asipe 5, faces a lateral surface 8 of an adjacent element 4, andcomprises at least one portion 9 sloping with respect to motiondirection 6 and mating with a corresponding portion 10 of lateralsurface 8. Given the slope of portions 9 and 10, one of them (portion 9in the example shown) faces an equatorial plane 1 a of tyre 1, while theother faces outwards of tyre 1.

Portions 9 and 10 are connected, in motion direction 6, by an elasticlocking device indicated as a whole by 11 and comprising an elasticappendix 12 projecting from portion 9 towards portion 10, and an elasticappendix 13 projecting from portion 10 towards portion 9. Appendixes 12and 13 lock on mutually, when portions 9 and 10 part in motion direction6. For which purpose, the appendix 12, 13 projecting from the portion 9,10 facing equatorial plane 1 a (appendix 12 in the example shown) islocated outwards of the other appendix 13, 12 with respect to equatorialplane 1 a.

Elastic locking device 11 also comprises a cavity 14 associated withappendix 12 and formed through portion 9 to receive appendix 13; and acavity 15 associated with appendix 13 and formed through portion 10 toreceive appendix 12. Each appendix 12, 13 is substantially in the formof a convex pyramid; each cavity 14, 15 is in the form of a concavepyramid; and each of appendixes 12 and 13 and the associated cavity 14,15 have respective coplanar, contiguous faces 16 a and 16 b, which areperpendicular to relative portion 9, 10, substantially radial withrespect to tyre 1, and mate with corresponding faces 16 b, 16 a of theother appendix 13, 12 and the other cavity 15, 14.

In actual use, parting of portions 9 and 10 in motion direction 6gradually compresses the pairs of faces 16 a and 16 b against each otherto limit expansion of relative sipe 5 in motion direction 6 incontrolled manner.

In the FIG. 2-4 embodiment, lateral surface 7 comprises at least twoportions 9 a and 9 b forming a concave angle A and mating withrespective portions 10 a and 10 b forming a convex angle B equal toconcave angle A .

In an embodiment not shown, the two portions 9 a and 9 b, and likewisethe two portions 10 a and 10 b, may be separated by a further portion oflateral surface 7 and 8 respectively. In the example shown, however,portions 9 a and 9 b are consecutive and adjacent, and define a concavedihedron 17 with a flare angle equal to concave angle A; portions 10 aand 10 b are consecutive and adjacent, and define a convex dihedron 18with a flare angle equal to convex angle B; and elastic appendixes 12are located between elastic appendixes 13.

1) A tyre, wherein the tread has a number of raised blocks divided intoa number of elements by sipes crosswise to a motion direction of thetyre; wherein each element has at least a first lateral surfaceextending along a said sipe and facing a second lateral surface of anadjacent element; the first lateral surface comprising at least onefirst portion facing and mating with a corresponding second portion ofthe second lateral surface; and the tyre being characterized bycomprising an elastic locking device for locking the first and secondportion to each other in the motion direction. 2) A tyre as claimed inclaim 1, wherein the elastic locking device comprises a first and asecond appendix, which are elastic, project from the first and secondportion respectively, and lock on mutually when said portions part inthe motion direction. 3) A tyre as claimed in claim 2, having anequatorial plane, and wherein said first and said second portion slopewith respect to the motion direction; one of said portions facing theequatorial plane, and the other facing outwards; and the appendix whichprojects from the portion facing the equatorial plane being locatedoutwards of the other appendix with respect to the equatorial plane. 4)A tyre as claimed in claim 2, wherein the elastic locking device alsocomprises a first and a second cavity associated with the first andsecond appendix respectively, and formed in the first and second portionrespectively to receive the second and first appendix respectively; eachof said first and second appendixes and the cavity associated with ithaving respective coplanar, contiguous faces, which are perpendicular tothe relative portion, are substantially radial with respect to the tyre,and mate with corresponding faces of the other cavity and of the otherappendix. 5) A tyre as claimed in claim 1, wherein the first lateralsurface comprises at least two first portions forming a concave angleand mating with respective second portions forming a convex angle equalto the concave angle. 6) A tyre as claimed in claim 5, wherein the twofirst portions are consecutive and define a concave dihedron with aflare angle equal to said concave angle; and the two second portions areconsecutive and define a convex dihedron with a flare angle equal tosaid convex angle. 7) A tyre as claimed in claim 2, wherein the twosecond appendixes are located between the two first appendixes.